1. Field of the Invention
The present invention relates to a machine tool in which a saddle is reciprocally movably disposed on a fixed bed. More particularly, the invention relates to the structure of the saddle.
2. Discussion of the Related Art
Among conventional machine tools there is, for example, a composite machining lathe in which one tool post is used for both lathe turning and rotating-tool machining. In this composite machining lathe, as shown in FIG. 4, on top of a fixed bed 200, a saddle 201 is disposed so as to be movable in the Z-axis direction (the perpendicular direction with respect to the plane of the drawing) by two linear guides 202. On top of the saddle 201, a column 204 is disposed so as to be movable by two linear guides 203 in a direction which is perpendicular to the Z-axis and in which the height increases with decreasing distance to the front (the direction indicated by arrow "a").
Further, on a front sloping surface 204a of the column 204, a tool post 205 is disposed so as to be movable in the X-axis direction and rotationally indexable to a specified angle. In addition, a headstock 206 is fixed to the fixed bed 200, and an automatic tool exchanger 207 is disposed on a sidewall of the column 204.
The saddle 201 is formed into a rectangular shape, as seen in a side view, with a height dimension (plate thickness) t unchanged from the front to the rear so that a line B interconnecting the linear guides 202 for the saddle and an axis line C of the linear guides 203 for the column are parallel to each other. Also, since heavy articles such as the column 204, the tool post 205 and the automatic tool exchanger 207 are mounted on the saddle 201, it is common practice to set the plate thickness t as large as possible to increase support.
However, increasing the plate thickness t of the saddle 201 as in the conventional lathe causes the height position of the tool post 205 to increase as well. As a result, the height h of the axis of the headstock 206 would become higher, which may deteriorate workability and machining precision.